How bad is too bad? As Ramsay Bolton, Iwan Rheon carved a path of destruction through Game of Thrones so memorably that it’s affecting relations with his fellow cast of Marvel’s Inhumans. Binge-watching co-star Serinda Swan’s reaction in the video interview above is almost as memorable. “Iwan, what are you doing?” she cries in mock horror. “You horrible man!” Apparently, his actions in Westeros are so bad, “I actually have to mute it and put it on one-bar fast forward.”

There’s considerably less cruelty in Rheon’s current role, which is something of a hallmark of Marvel productions. Though based in the flat, four-color world of comic books, Marvel takes pains to create nuanced villains who have good reasons for the things they do. In this case, Rheon’s powerless Maximus wants to overthrow the royal family — led by his brother, Black Bolt (Hell on Wheels‘ Anson Mount), and sister-in-law, Swan’s Medusa — in a coup.

There’s also a reason why Medusa can handle herself in a fight. “She was not born a queen; she just happened to marry into it,” Swan says. Medusa’s parents were exiles, which means she was forced to survive on the streets for a time. That explains why — at the end of the second episode when she’s been chased to Earth and cornered by her pursuer — she lashes out in an exceptionally violent way.

“When we were doing it the first time, I just stabbed her once. And they were, like, ‘Maybe give it a couple stabs.’ ‘A couple as in two? Or, like, a few as in three or more?’ And they were, like, ‘No, no — a few,'” she says. “Okay, so I stabbed her four times. And they’re, like, ‘We’re thinking more like eight.’”

“There is no clear black and white on this show,” Swan concludes. “I think if you were to lay out their belief systems, most people would side with Maximus.” And Medusa herself? Even though they are at odds, she can’t help but consider his side. “She was upholding something that she doesn’t necessarily believe in, and I think the revolution that Maximus brings to Attilan starts to make her question her own beliefs, her own actions,” she says.

Medusa’s most striking characteristic is her long hair, so it can be startling to see Swan as she is now — sporting a platinum blond buzz cut as a result of filming. It was a drastic change (“My head was shaved days into getting [to set],” she says), but she was more than ready.

“I’ve always wanted to have my head shaved,” she says. “Actually, when Marvel asked if I was okay with it, I was, like, ‘Not only am I okay, but I happen to have a photoshopped image of my face on Natalie Portman’s head from a few years ago when I was trying to do it back then!’”

Of course, since this is Marvel, Swan was contractually obligated to keep her shorn head a secret. “’You get to shave your head.’ ‘Yay! This is the best thing ever! My inner tomboy is so happy!’ ‘Yes, but you have to wear a wig until September first, and nobody can see it.’ So, it was this amazing thing to happen, but then also I was devastated that I had to figure out how to wear a wig while it was boiling hot in Hawaii,” she says.

Another challenge unique to this show is having to act with someone, Mount, whose character can’t speak (Black Bolt’s voice can cause destruction and death). “My audition scene was… I say it was a scene, but it was really just a monologue,” Swan says. “It was walking into a room and having a conversation with nobody, basically.” And the challenge increased exponentially when she actually got the role.

“It was figuring out how to represent two people in a scene, leave enough stillness and silence while he’s speaking that it’s new information,” she says. “Even though I’ve learned his lines — I know what he’s saying, I know how I’m going to have to say them — I still had to act as if I didn’t and do it in silence. Which is not normal!”

It was Mount who found the best way to sum up her character. With the assistance of sign language experts, he created his own system of signs, and for Medusa, Swan says, “It’s this twist by his neck and then he pulls his hand down to heart, so it’s a mixture of the hair and the heart.”

Marvel’s Inhumans premieres with additional footage not seen on IMAX screens Sept. 29 at 8 p.m. on ABC.